Differentiated services are a suitable solution to Quality of Service (QoS) provisioning in the Internet while the number of users keeps growing. The solution is suitable, because it scales well with increasing number of network users and it does not alter the current Internet paradigm much. In this article, we review the state of the art in this new area, and compare some of the main existing differentiated services architectures. We outline the common solutions across these architectures, thus paving the road to a unified architecture. Lastly, we mention the issues that have not been thoroughly addressed yet.